science lesson

Schrodinger came up with the quantum theory that the state of particles could best be described in probability fields. Rather than saying with certainty where a particle is, we can only say with varying degrees of probability where it is; thus a particle potentially exists in many places at the same time.

Suppose that your computer is the range of all probability, and we're trying to track a quantum particle as it travels from the top middle of your screen to the bottom middle. From past experience, we know that 40 percent of the time, our chosen particle travels a route somewhere within the middle third of your screen. Next to that middle third are paths it has taken in the past with less frequency. Maybe the next strip on each side has been traveled 20 percent of the time, and the strip after that only 5 percent of the time, and so on, out to the edges where there is only an infinitessimal probability that our quantum particle will travel that route. (More or less your standard bell curve distribution.)

This quantum field is actually useful for some sort of mathematical/physics thing I dimly remember from some reading I did in high school.

Anyway, Shrodinger, whose umlauts I am too lazy to recreate at this point, illustrated his principle with this suggested mechanism: Take a cat and put it in a box. Elsewhere there is a radioactive isotope that is going to decay; at the point it decays, a poison gas will be released into the box where the cat is, and the cat will die. You have no way of knowing the state of the particle and therefore have no way of knowing if the cat is alive or dead.

Time elapses. At this point, there is a 10 percent chance the isotope has decayed. Is that cat alive? There's a 90 percent chance it is.

More time elapses. The isotope has a 25 percent chance of having decayed. Is that cat alive, or is it dead? There's a 75 percent chance it is alive, and a 25 percent chance we will need to explain to the university president why it was necessary to poison a cat during a physics lecture.

For purposes of the experiment, the cat as an entity does not exist. It exists in a state of probability; it may be a cat, or it may be that it wouldn't voom even if you put 80,000 volts of electricity through it. For this reason, the principle of probability in quantum mechanics became known as Schrodinger's Cat.

Fred Pohl (?) did a fairly decent -- or so it seemed at the time, to me -- sci-fi novel where he applied Schrodinger's ideas to spacetime, where we know the startpoint and endpoint of the universe, from Big Bang to Big Crunch. Which path does the universe take in-between? Well, we live upon one probability strand, but there are other timelines of other probabilities -- alternate timelines, where history worked out differently. On those, you will find Americas where 9-11 was prevented, or ones where Gore was president and it happened. On still others, Bill Bradley or John McCain was president at the time of 9-11. There is another timeline exactly like the one we are in now, but I used a different example of the timelime, or didn't fix my typo in the word "example," and so on. In Pohl's novel, and in later books too, I believe, people who travel across those probability lines, from one alternate history to another, are called Quantum Cats.

And this concludes today's lesson in quantum theory.